Sludge treatment method

Abstract

A sludge treatment method allowing an improvement in a phosphorus recovery rate and sludge volume reduction by efficiently eluting phosphorus in the sludge. The sludge treatment method includes: a step of foaming a sludge-containing liquid by blowing an ozone-containing gas into the sludge-containing liquid; and a step of eluting phosphorus in the sludge-containing liquid by bringing sludge adsorbed on bubbles and a sludge-dissolving agent into contact with each other. The sludge treatment method may further include the steps of: separating the phosphorus eluted sludge-containing liquid into a phosphorus eluate and a residual sludge; and precipitating a phosphorus compound by adding a coagulant to the separated phosphorus eluate.

1. A sludge treatment method, comprising the steps of:
 foaming a sludge-containing liquid by blowing an ozone-containing gas into the sludge-containing liquid to generate sludge-adsorbed bubbles and discharge the bubbles from a bubble discharge port provided in an upper portion of an ozone treatment vessel, wherein the ozone-containing gas is blown into the sludge-containing liquid during the foaming step using a diffuser pipe provided at the bottom of the ozone treatment vessel, and wherein the foaming step further includes mixing the sludge-containing liquid and the bubbles using a bubble mixing blade provided at an upper portion of the ozone treatment vessel and a liquid mixing blade provided at a lower portion of the ozone treatment vessel; 
 eluting phosphorus in the sludge-containing liquid by supplying the bubbles to a phosphorous elution vessel from the bubble discharge port thereby bringing sludge adsorbed on the bubbles and a sludge-dissolving agent into contact with each other within the phosphorous elution vessel; and 
 decomposing waste ozone gas not dissolved in the sludge-containing liquid into oxygen, wherein the waste ozone gas is received from an upper portion of the phosphorous elution vessel. 
 
     
     
       2. A sludge treatment method according to  claim 1 , further comprising the step of:
 precipitating a phosphorus compound by separating the phosphorus eluted sludge-containing liquid into a phosphorus eluate and a residual sludge and by adding a coagulant to the separated phosphorus eluate. 
 
     
     
       3. A sludge treatment method according to  claim 1 , further comprising the step of:
 discharging the oxygen into the atmosphere. 
 
     
     
       4. A sludge treatment method according to  claim 1 , further comprising the step of:
 accelerating phosphorus elution by mixing the phosphorous eluted sludge-containing liquid. 
 
     
     
       5. A sludge treatment method according to  claim 4 , further comprising the step of:
 circulating sludge between the phosphorous elution vessel and a phosphorous elution acceleration vessel within which the accelerating step is performed. 
 
     
     
       6. A sludge treatment method according to  claim 4 , further comprising the step of:
 precipitating a phosphorus compound by separating the phosphorus eluted sludge-containing liquid into a phosphorus eluate and a residual sludge and by adding a coagulant to the separated phosphorus eluate. 
 
     
     
       7. A sludge treatment method according to  claim 1 , further comprising the steps of:
 receiving residual liquid from the foaming step that was not adsorbed on the bubbles; and 
 accelerating phosphorus elution by mixing the phosphorous eluted sludge-containing liquid and the residual liquid. 
 
     
     
       8. A sludge treatment method according to  claim 7 , further comprising the step of:
 circulating sludge between the phosphorous elution vessel and a phosphorous elution acceleration vessel within which the accelerating step is performed. 
 
     
     
       9. A sludge treatment method according to  claim 7 , further comprising the step of:
 precipitating a phosphorus compound by separating the phosphorus eluted sludge-containing liquid into a phosphorus eluate and a residual sludge and by adding a coagulant to the separated phosphorus eluate. 
 
     
     
       10. A sludge treatment method according to  claim 1 , further comprising the steps of:
 receiving residual liquid from the foaming step that was not adsorbed on the bubbles; and 
 accelerating phosphorus elution by bringing the residual liquid and a sludge-dissolving agent into contact with each other. 
 
     
     
       11. A sludge treatment method according to  claim 10 , further comprising the step of:
 circulating sludge between the phosphorous elution vessel and a phosphorous elution acceleration vessel within which the accelerating step is performed. 
 
     
     
       12. A sludge treatment method according to  claim 1 , wherein the eluting phosphorous step further includes mixing phosphorus eluted sludge-containing liquid within the phosphorous elution vessel. 
     
     
       13. A sludge treatment method according to  claim 12 , wherein the mixing is performed using at least one liquid mixing blade provided at a lower portion of the phosphorous elution vessel and at least one defoaming blade provided above the at least one liquid mixing blade. 
     
     
       14. A sludge treatment method according to  claim 13 , wherein a greater number of defoaming blades are provided in the phosphorous elution vessel than liquid mixing blades.